Fluid storage systems have been in existence for many years, specifically underground storage systems for the collection and storage of water. While water is collected underground for various reasons, over the past 20 years there has been increased focus on collecting and storing storm water runoff. This is done because of two main concerns. The quantity of storm water runoff is a concern because larger volumes of associated runoff can cause erosion and flooding. Quality of storm water runoff is a concern because storm water runoff flows into our rivers, streams, lakes, wetlands, and/or oceans. Larger volumes of polluted storm water runoff flowing into such bodies of water can have significant adverse effects on the health of ecosystems.
The Clean Water Act of 1972 enacted laws to improve water infrastructure and quality. Storm water runoff is the major contributor to non-point source pollution. Studies have revealed that contaminated storm water runoff is the leading cause of pollution to our waterways. As we build houses, buildings, parking lots, roads, and other impervious surfaces, we increase the amount of water that runs into our storm water drainage systems and eventually flows into rivers, lakes, streams, wetlands, and/or oceans. As more land becomes impervious, less rain seeps into the ground, resulting in less groundwater recharge and higher velocity surface flows, which cause erosion and increased pollution levels in water bodies and the environment.
To combat these storm water challenges associated with urbanization storm water detention, infiltration and retention methods have been developed to help mitigate the impact of increased runoff. Historically, open detention basins, wetlands, ponds or other open systems have been employed to capture storm water runoff with the intention of detaining and slowly releasing downstream over time at low flows using outlet flow controls, storing and slowly infiltrating back into the soils below to maximize groundwater recharge or retain and use for irrigation or other recycled water needs. While the open systems are very effective and efficient, the cost of the land associated with these systems can make them prohibitive. In areas such as cities or more densely populated suburbs the cost of land or availability of space has become limited. In these areas many developers and municipalities have turned to the use of underground storage systems which allow roads, parking lots, and building to be placed over the top of them.
A wide range of underground storage systems exist, specifically for the storage of storm water runoff. Arrays of pipes, placed side-by-side are used to store water. Pipe systems made of concrete, plastic or corrugated steel have been used. More recently arched plastic chamber systems have been in use. As with pipes, rock backfill is used to fill the space surrounding them to create added void areas for storing additional water along with providing additional structural reinforcement.
In general, these types of systems require at least one foot of rock backfill over the top and at least one or more feet of additional native soil over the top to support the loading associated with vehicles on streets and parking lots. These systems also require rock backfill of a foot or more around their perimeter sides to provide structural reinforcement due to lateral loading associated with soil pressure.
Lastly, these systems must also be placed on a rock base for structural support. Because these systems are rounded or arched, a substantial amount of rock backfill must be used to surround them and placed in between the systems. As such, the amount of void space available for storing water compared to the amount of soil required to be excavated is only around 60 percent.
Over time, plastic and concrete rectangular or cube shaped modular systems were developed that more efficiently stored storm water because the modules could be placed side-to-side and end-to-end without the need for additional rock backfill to be placed between each module as found with pipe and arched systems. With these rectangular and cube shaped systems the void space available for storing water compared to the amount of soil required to be excavated is up to 90% or more. While plastic type rectangular and cubed systems still require at least two feet of rock backfill over the top, two feet around the perimeter sides, and six inches underneath to handle downward and lateral loading, the concrete rectangular and cubed systems do not.
Concrete rectangular or cubed modular systems have the benefit of not requiring rock backfill over the top or surrounding the sides because of their additional strength when compared to plastic systems. For example, currently available concrete systems can have the bottom of the structure as deep as eighteen feet below surface level standard wall thickness. The thickness of the structure can increase from six inches to eight inches or more plus adding additional rebar reinforcement to allow for deeper installation.
Most concrete rectangular or cube shaped structures have five sides, four vertically extending walls and a bottom or top side. One side must be open because of how pre-cast concrete molds are made and how the concrete structure is pulled from the mold. At least one side of the concrete structure must be missing for it to be pulled from the metal mold that consists of inner and outer walls and either a top or bottom side.
Unfortunately, this missing side which is required for manufacturing, creates an inherent weak point for the walls. The middle of each wall, especially the longer walls for rectangular structures, where the wall meets the end of the missing top or bottom side has no perpendicular connection as with the opposite side of the same wall where it connects to the top or bottom side. This weak point on the center of each wall at the open end is the reason why these systems have depth limitations. This is known as deflection. This weak point becomes further exaggerated the taller the wall becomes and the longer it becomes; the further away it is from the perpendicular connecting floor or adjacent wall on the opposite end. Therefore, taller systems which extend down deeper from the surface underground run into a compounding problem of taller walls and increased lateral loading (soil pressure).
Recently, an approach to the aforementioned technical problem has been to replace solid wall chambers with cantilever, or semi-arched arm braces, to support the top module. This approach falls short of addressing common problems in the industry as these systems still cannot sustain increased soil pressure and lateral loading due to its shape without need to increase the wall thickness of the modules or increase the amount of rebar reinforcing therefore increasing material and overall cost of deep installations. The present technology presents a novel approach to addressing common industry limitations.
The need for a system overcoming these inherent shape-related limitations is evident. The present invention provides an exemplary solution including the method, system, and apparatuses derived from principles of biomimetics; specifically, the employment of tesselated modular assembly. The construction of interlinking mosaic shapes and material layering increases the strength of the modular assembly by reducing crack propagation; thereby allowing the assembly to be underground at greater depths than underground water storage systems known in the art. This type of geometric arrangement also overcomes potential structural weakness of an individual module, as a result of manufacturing errors or transport mishaps. Mosaic configurations disclosed herein also mitigate swelling pressure of ambient soil due to the segmentation design. Paving roads with small segmented materials such as brick or paving stones, as an example, has long been utilized to withstand soil swelling.
Design inspired by these efficient structures found in nature and the employment these more economic natural shapes, in combination with current precast concrete design processes, present a unique approach for overcoming the limitations of the previous approaches in the industry.